Iranian Journal of Chemical Engineering (IJChE)

Abstract This study investigates the performance of an electrodialysis metathesis (EDM) process using polyvinyl chloride/carbon nanotube (PVC/MWCNTs) nanocomposite ion-exchange membranes (IEMs) for simultaneous water desalination and chemical production. IEMs with MWCNTs loadings of 0% (M1), 4% (M2), 8% (M3), and 10% (M4) by weight were fabricated and characterized for water sorption, areal electrical resistance, hydrophobicity, and mechanical strength. Their ion selectivity, separation performance, desalination efficiency, and production yield were systematically evaluated under varying applied voltage, feed composition, and operation time. Among the fabricated membranes, M3 (8 wt% MWCNTs) exhibited the best performance, providing optimal ionic conductivity, selectivity, and structural stability. Maximum chemical yield was achieved when solute concentrations in the electrode chambers exceeded those in the desalination chamber. In contrast, M4 (10 wt% MWCNTs) showed reduced efficiency, attributed to MWCNTs agglomeration and pore blockage that hindered ion transport. Increasing voltage improved ion transport up to an optimal level, but excessive voltage (15 V) caused water splitting and concentration polarization, lowering both chemical yield and desalination efficiency. These results highlight the importance of MWCNTs loading optimization and controlled operating conditions. Overall, PVC/MWCNTs composite IEMs exhibited significant potential for integrated chemical production and saline wastewater treatment, providing a cost-effective and scalable strategy for resource recovery.

Abstract This study evaluates the effectiveness of the aluminum sulfate coagulation in treating the wastewater from thermal power plants to efficiently remove pollutants. Key operational parameters—the pH of the wastewater (5 to 9), dosage of coagulant (10 to 40 mg/L), and mixing time (10 to 30 minutes)—were systematically investigated for their impact on the removal of chemical oxygen demand (COD) and total dissolved solids (TDS). The coagulation mechanism involves the hydrolysis of aluminum sulfate, generating charged species that neutralize particle charges, followed by adsorption, bridging, and floc formation, which together promote the aggregation and sedimentation of pollutants. Utilizing the response surface methodology (RSM) with the Design Expert software, the process was optimized, revealing that a pH near 7.4, dosage of approximately 40 mg/L of the coagulant, and mixing time of around 22 minutes maximize the treatment efficiency. Under these conditions, the removal of COD and TDS reached 71.1% and 97.3% respectively, demonstrating the potential of this approach for the sustainable and cost-effective wastewater treatment in thermal power plant operations.

Abstract The Fe₃O₄/MW-CNT composite was prepared for a hybrid photo-catalyst-assisted electrochemical process for the removal of BTX contamination from wastewater. Oxidation of multi-walled carbon nanotube was conducted by different treatments including acid treatment and hydrogen peroxide. The XRD, FTIR, SEM, TEM, and BET analyses were performed to characterize both the MW-CNT and the synthesized composite. Simultaneous photo-catalyst and electrochemical processes were conducted to evaluate the performance of a new hybrid process for wastewater treatment. The effect of current density, photo-catalyst loading, and BTX initial concentration was investigated experimentally. The characterization results of the synthesized composite show that a mixture of strong nitric acid and sulfuric acid treatment at a high exposure time and low temperature is the best route for MW-CNT oxidation. The removal efficiency of BTX compounds from wastewater using the hybrid photo-electrochemical process was found to be in the range of 28 to 43% for different conditions. The optimum condition for maximum removal of BTX was found by mathematical modeling of experimental data. The results indicate that a combination of photo-catalyst and the electrochemical process can enhance the BTX removal efficiency.

Abstract This study was conducted to decrease the concentration of acetic acid in wastewater of acetic acid plants through the photocatalytic oxidation method. This process employed commercial Titanium dioxide powder (TiO₂) as a photocatalyst, utilizing a UV lamp as the light source within a batch reactor system for advanced oxidation. Various experimental parameters were modified, including the concentration of acetic acid, the amount of catalyst, the volume of waste, temperature, and reaction time. The residual acid concentration and COD values were recorded as results of the process. The percentage of acetic acid remaining in the solution was determined by using a gas chromatography (G.C) device. Experiments were conducted with different volumes, from 200 ml to 35 ml, and utilized varying amounts of photocatalyst: 0.01 g, 0.005 g, 0.0025 g, and 0.001 g. Additionally, the experiments were carried out over two-time intervals of 2 hours and 5 hours. The wastewater concentration contained 3% by mass of acetic acid, and the average COD value was 13300. After experiments, it was found that the optimal conditions for removing acetic acid were a volume of 35 ml and 0.0025 g of catalyst used for 2 hours. In this condition, the percentage of acetic acid decreased from 3% to 0.2%, which is a 93% decrease, and the COD decreased from 13,300 to 2,800, which is a 79% decrease.

Abstract Constructed wetlands have been increasingly used as an effective method for removing heavy metals from wastewater. This study aimed to investigate the combined effect of sawdust and Hydraulic Retention Time (HRT) on the performance of vertical-flow constructed wetlands cultivated with Phragmites Australis to remove Pb and Co from oily wastewater. To this end, nine barrels were used to construct the wetlands, which were filled with coarse gravel, polluted soil, and varying percentages of sawdust (0%, 20%, and 40%). Phragmites Australis cuttings were then cultured inside the barrels and irrigated with heavy metal-contaminated oily wastewater for three different hydraulic retention times (5, 10, and 15 days). After the vegetation period, plant, soil, and wastewater samples were collected and analyzed for Co and Pb concentrations, from which transfer factor (TF), bioconcentration factor (BCF), and removal efficiency (%) were derived. Results showed that while both Pb and Co removal efficiencies were affected by HRT and sawdust, the removal efficiency of Pb (36.66%) was higher than that of Co (30.83%). TF was less than one and was not affected by HRT and sawdust, but the effect of HRT and sawdust on increasing BCF was significant. However, Phragmites Australis demonstrated suboptimal performance in the uptake and transfer of metals from the root to stem.

Abstract The properties of the Nanoclay-corn starch film were studied in the presence of Nanostarch. Nanostarch was synthesized through nanoprecipitation and characterized using the Particle Size Distribution Analysis, Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction Analysis (XRD), and Fourier Transform Infrared Analysis (FTIR). The XRD analysis of nanostarch particles revealed a distinctive V-type diffraction peak, with particle diameters ranging from 25 to 100 nm. The impact of introducing nanostarch into the starch-nanoclay film was investigated in terms of the thickness, transparency, morphology, wettability, and mechanical properties of the nanocomposite film. The results indicated that adding nanostarch particles improved the optical transparency of the film along with its hydrophobicity and flexibility. The film having a weight ratio of 0.769 (nanoclay to nanostarch) showed the maximum hydrophobicity (107.85°), and elongation at break (58.6%). This suggests that the appropriate incorporation of nanostarch can enhance the film's flexibility. The maximum tensile strength (5.88 MPa) was obtained for the film with a weight ratio of 1 (nanoclay to nanostarch).

Abstract The membrane bioreactor (MBR) is a combination of biological and membrane systems. It utilizes advanced technologies in the treatment of various types of wastewater, having unique advantages such as the high-quality effluent and improved efficiency. The primary limiting factor for the utilization of this bioreactor  is the  membrane fouling phenomenon, which increases operational costs. In this study, four membrane bioreactors were used, with the first MBR (R1) serving as the control bioreactor. In the second MBR (R2), an adsorption process was employed, while in the third (R3) and fourth MBR (R4), in addition to the adsorption process, the electrochemical process was applied with voltages of two and one volts respectively. For the four bioreactors, the percentages of the Chemical Oxygen Demand (COD) were recorded as 86%, 91.2%, 90.7%, and 95.3% respectively. The levels of the total Extracellular Polymeric Substances (EPS) in R1, R2, R3, and R4 were about 260, 155, 177, and 98 mg/gVSS respectively. The R4 exhibited significantly lower EPS (98 mg/gVSS) compared to R1 (260 mg/gVSS), possibly due to the adsorption of EPS by nanoparticles and its subsequent removal during the electrochemical process. The role of voltage was evident in R3, where the higher voltage (2V) resulted in the less removal of EPS (155 mg/gVSS) compared to the same in R4 (98 mg/gVSS). The study found that the values of the Soluble Microbial Products (SMP) for R4, R3, R2, and R1 were about 15, 65, 55 and 139 mg/L respectively. Particularly in the most effective MBR, R4, where the addition of the zeolite adsorbent alongside metal ions demonstrated the best performance in the removal of SMP.

Abstract The Fe3O4/MW-CNT composite was prepared for a hybrid photo-catalyst-assisted electrochemical process for the removal of BTX contamination from wastewater. Oxidation of multi-walled carbon nanotube was conducted by different treatments including acid treatment and hydrogen peroxide. The XRD, FTIR, SEM, TEM, and BET analyses were performed to characterize both the MW-CNT and the synthesized composite. Simultaneous photo-catalyst and electrochemical processes were conducted to evaluate the performance of a new hybrid process for wastewater treatment. The effect of current density, photo-catalyst loading, and BTX initial concentration was investigated experimentally. The characterization results of the synthesized composite show that a mixture of strong nitric acid and sulfuric acid treatment at a high exposure time and low temperature is the best route for MW-CNT oxidation. The removal efficiency of BTX compounds from wastewater using the hybrid photo-electrochemical process was found to be in the range of 28 to 43% for different conditions. The optimum condition for maximum removal of BTX was found by mathematical modeling of experimental data. The results indicate that a combination of photo-catalyst and the electrochemical process can enhance the BTX removal efficiency.

Abstract Optimization of the homogeneous rhodium-catalyzed methanol carbonylation reactor to reduce CO2 emissions is studied in this line of research. In this paper, the steady-state homogeneous rhodium-catalyzed methanol carbonylation reactor is simulated using Aspen HysysV.9 software, by comparing the simulation results with industrial information, a mean relative error (excluding methanol) of 4.8% was obtained, which indicates the high accuracy of the simulation. The central composite design (CCD) and genetic algorithm (GA) with the aid of a simplified process simulation were used to estimate the effect of individual variables (liquid level, the temperature of the catalyst-rich recycle stream, the mole ratio of CO to methanol (MeOH) in the feed, and flow rate of dilute acid stream) and their mutual interactions to reduce CO2 emissions. It is obtained that the liquid level percentage of 46%, the catalyst-rich recycle stream temperature of 120 °C, CO: MeOH molar ratio equal to 1.13:1, and the dilute acid flow rate of 513.14 kmol/hr lead to CO2 reduction by 34%.

Abstract The size and lifetime of evaporating sneeze droplets in the indoor environment were studied experimentally and theoretically. The effects of indoor temperature T_∞ and indoor humidity RH_∞ on evaporating droplets with the initial diameters of 4.9, 8.1, 17.2, and 29.7 μm were investigated. The size distribution and mean size of droplets were obtained by a laser particle sizer. The experimental data showed that the possibility of aerosolized droplets increased from 25.5 to 36.1 % by increasing T_∞ from 18 to 30 °C and decreased from 36.1 to 13.6 % by increasing RH_∞ from 30 to 60 %. A one-dimensional droplet evaporation model was used to estimate the lifetime of the droplet. A critical RH_∞ of 40 % was found; above it, the lifetime of the droplet exponentially increases. The effect of the initial diameter of droplets was higher than that of RH_∞ and also the impact of RH_∞ was higher than that of T_∞ on the lifetime of the aerosolized droplet nuclei. A significant effect of environmental conditions on the lifetime of the droplet was found over the range of 26 °C ≤ T_∞ ≤ 30 °C and RH_∞ ≤ 40 %, while the effect decreased in the range of 18 °C ≤ T_∞ ≤ 22 °C and RH_∞ > 40 %, where a minimal shrinkage of droplets took place because of the hygroscopic growth of droplets. The results of this study do not imply that the COVID-19 virus will be deactivated at the end of the lifetime of the droplet, but it represents that controlling the indoor environment is important for droplets to carry the virus.

Abstract In this research, silica gel as a low-cost adsorbent for the uptake of carbon dioxide was investigated experimentally. The samples were characterized by XRD, BET and FT-IR. It shows that as pressure was increased from 2 to 8 bar, the CO2 adsorption capability improved over time. At a pressure of 6 bar and a dose of 1 g of silica gel, the impact of temperature (25, 45, 65, and 85 °C) on the CO2 adsorption capacity (mg/g) was determined. The process behavior was investigated using isotherm, kinetics and thermodynamic models. As the temperature rises at a constant pressure, the adsorption capacity decreases. The experimental data of the carbon dioxide adsorption using silica gel have a high correlation coefficient with both Langmuir (0.998) and Freundlich (0.999) models. The results of the carbon dioxide adsorption kinetics with the silica gel adsorbent show that the correlation coefficient (R2) of the second-order model and Ritchie's second model are equal to 0.995 and have the highest value. The total pore volume was 0.005119 (cm3 g-1) and the specific surface area was 2.1723 (m2g−1). The maximum CO2 adsorption capacity at 25 °C near 8 bar was 195.8 mg/g.

Abstract The central composite design (CCD) was employed to investigate the adsorption of Pb(II) and Zn(II) metal ions as well as methylene blue (MB) as an aromatic anion by a new EDTA/MnO₂/CS/Fe₃O₄ synthesized nanocomposite. The effect of possible affective factors including the contaminant concentration (20-200 mg/L), pH (2-8), adsorbent content (0.1-0.9 g/L), and contact time (10-110 min) on the adsorption of the metal ions using response surface methodology (RSM) were studied. The highest removal percentages predicted by the model were 100.776 % and 87.069 %, respectively, for the removal of Pb(II) and Zn(II), that the value of more than 100 % in the case of Pb(II) was due to the model’s error. The effect of the simultaneous presence of methyl blue (MB) and the metal ions in the aqueous solution on the adsorption rate of each metal ion was investigated. The study of the adsorption isotherms in the single-component adsorption showed the dominance of Langmuir isotherm over the adsorption process of each pollutant (R² > 0.99). The maximum adsorption capacities according to the Langmuir model were 310.4 and 136 mg/g for lead and zinc ions, respectively, and 421.1 mg/g for methyl blue. The results showed that the studied nanocomposite still had high efficiency after five consecutive adsorption-desorption cycles

Abstract Ziziphus nuts are abundant in Khuzestan province, Iran, and are considered as an unwanted natural biomass waste. The present study is aimed to develop low-cost activated carbon from Ziziphus nuts as a new precursor for the removal of phosphate from the water environment.the iron oxide modification was performed to simultaneously facilitate the adsorbent separation via a simple magnetic process and increase the phosphate removal capacity. The iron oxide/activated carbon composite (IOAC) was characterized using XRD, EDX, SEM, and BET methods. The specific surface area for IOAC reached 569.41 m²/g, comparable to that of the commercial activated carbon. While other similar derived-from-biomasses activated carbon reached the phosphate removal capacity of around 15 mg/g, IOAC demonstrated the excellent phosphate removal performance of as high as 27 mg/g. Also, IOAC showed fast adsorption kinetics, achieving equilibrium in only 60 minutes. According to the results, the pseudo-second-order kinetic model was more consistent with the data related to the phosphate adsorption onto the adsorbent than the pseudo-first-order model. The adsorption results using Langmuir, Freundlich, and Webber-Morris diffusion models were interpreting. The maximum Langmuir adsorption capacity was calculated to be 27 mg/L. The adsorbent was removed from the aqueous solution via a simple magnetic process.

Abstract Due to the dangerous effects of sulfur in hydrocarbon compounds and its impact on environmental health, a new formulation based on surface-modified carbon nanotubes and a cobalt oxide has been prepared. Oxidative desulfurization is the main section of this process that is utilized to reduce this impurity. After decorating cobalt oxide on the surface of nanotubes, the TEM images and Thermogravimetric analysis were studied to evaluate the structure of this complex. The results show that the combination of metal oxide and functionalized nanoparticles presents better efficiency in sulfur removal. In addition, the reaction rate raised by increasing the number of functional groups on the surface of nanotubes. Then, the influence of temperature, reaction time and the concentration of the oxidizing agent in the sample was investigated. The results show that the higher temperature and higher number of oxidizing agents could provide better efficiency in the desulfurization process. Due to the presence of CNTs in the synthesized catalyst, it is possible that sulfur compounds adsorbed with CNT. By matching the data with the Pseudo first and second order adsorption kinetic, it was found that the adsorption is done as a Pseudo first order adsorption kinetic. Since the ODS process is performed by a chemical reaction, the reaction kinetics were adapted to the first order equation and calculate the activation energy required for the reaction. This result can be utilized for better desulfurization of hydrocarbon fuels for different applications.

Abstract Many communities in the world use groundwater as a source of potable water. The high nitrate concentration is a serious problem in groundwater usage. This study utilizes a biological denitrification method to investigate a moving bed biofilm reactor (MBBR) for the case of Tehran's groundwater. One pilot-scale MBBR with a 3 liter volume was designed and used in this research. The denitrification reactor operates under anoxic conditions. Methanol was used as a carbon source in the reactor throughout the study, and fifty percent of the reactor volume was occupied with KMT packing (k₁). To determine the optimum nitrate loading rate, the concentration of nitrate changed from 100 to 400 mg N/l. It was concluded that heterotrophic denitrifying bacteria converted nitrate to nitrogen. According to obtained results, the removal efficiency and optimum loading rate were estimated during the experiments in different concentrations and different HRTs for this type of reactor. Sodium nitrate was in the feed source in the anoxic reactor. The maximum removal rate of nitrate was measured to be 2.8 g of NO₃-N m^-2 carrier d^-1. Therefore, it was shown that the optimum loading rate of nitrate and the optimum COD/N were equal to 3.2 g of NO₃-N m^-2 carrier d^-1 and 6 g of COD/g N respectively.

Abstract In this work, performance of hollow fiber membrane photobioreactor (HFMPB) on the growth of Dunaliella Salina (G26) at various aeration rates (0.1 and 0.2 VVm) and medium re-circulation flow rates (500 and 1000 mL/h) were studied. Cultivation was carried out at both batch and semi-continuous modes in HFMPBs containing neat and hydrophilized in-house fabricated poly ethylene (PE) membranes at fixed light intensity of 300 µmol m-2 s-1and temperature of 30 oC. Microalgae showed better growth in hydrophobic module in both cultivation modes and modules. Maximum biomass concentration, CO2 biofixation and specific growth rates equal with 0.71g L-1, 1.102g L-1 d-1 and 0.224d-1 were obtained for non-wetted membranes, respectively. Comparing the performance of both modules showed that the impact of cultivation mode on the CO2 biofixation rate and CO2 removal is more pronounced than the impact of mass transfer resistance in membrane contactors. The obtained results show that the mean CO2 biofixation rates in semi-continuous cultivation for both neat and hydrophilized modules are higher than that in batch cultivation in all operating conditions. It was also found that the hydrophobic membranes are much preferable than hydrophilic membrane in HFMPBs.

Abstract Airborne particulate matter (PM₁₀ ) was collected from the atmosphere of the city of Isfahan. The concentration of heavy metals and anions associated with airborne particulate matter were determined using atomic absorption spectrometric and ion chromatographic techniques. A comparison was made between the variation in the concentration of PM₁₀ and that for heavy metals and CO. An excellent similarity was found between the variation model of PM_10, heavy metals and CO. Due to the atmospheric concentrations of heavy metals, the enrichment factors were calculated and showed that the well-known toxic heavy metals are mostly released into the city atmosphere from anthropogenic sources.
 
 
 

Abstract This article presents the research results on production and performance of palladium-only catalytic converters. Monolith is used as the catalyst carrier and gamma alumina as the substrate. Dipping method is used for monolith washcoating. Palladium as the active metal is impregnated on gamma alumina using wet impregnation to produce catalyst samples. The effects of factors such as percent solids in slurry, milling time, calcination time and temperature, pH and existence of Al(NO3)3 on wash-coat characteristics were studied experimentally. SEM, XRD and BET tests were carried out on the samples. Catalyst performance was tested in an experimental reactor that was designed for this research. The results show that catalytic activity increases as calcination time increases, whereas it declines as calcination temperature increases. Furthermore, as the slurry pH decreases, the catalytic activity also decreases. It was observed that impregnation of Al(NO3)3 does not have any effect on catalytic activity.